Steel wire cage wire for chemically prestressed concrete pipe

ABSTRACT

A wire used in the wire cage of chemically prestressed concrete pipe is effective to restrain the expansion of expansion concrete over a wide range and with a uniform stress during the manufacture of the pipe. The plane of the wire which applies stress to the concrete is approximately straight or mildly curved in section, its width being larger than the diameter of a circular wire having the same cross sectional area and its thickness being smaller than said diameter. The plane which acts on the concrete is provided with projections for spot welding in the formation of the wire cage.

United States Patent Mizuma [451 Apr. 11, 197 2 541 STEEL WIRE CAGE WIRE FOR 1,255,678 2/1918 Witherow ..52/734 I A Y PRESTRESSED 1,763,360 6/1930 Kean ..138/ 176 x 1,910,643 5/1933 Shurard ..138/176 CONCRETE PIPE 2,069,280 2/1937 Schuster ..52/653 X [72] Inventor: Katsuhisa Mizuma, Fujisawa, Japan 2,660,199 11/1953 Montgomery" .....138/l76 X [73] Assignee: KoushuhaNesuren Kabushiki Kaisha 2,870,626 1/1959 G1llberg ..52/734 Tokyo Japan Primary Examiner-Herbert F. Ross [22] Filed: Feb. 18, 1970 Attomey-Wenderoth, Lind & Ponack [30] Foreign application Priority pata 7 A wire used in the wire cage of chemically prestressed concrete pipe is effective to restrain the expansion of expan- Mar. 13 1969 Japan 44 l 85Zl sion concrete over a wide range and with a uniform stress ing the manufacture of the pipe. The plane of the wire which E (g! BS/17: 1 applies stress to the concrete is approximately Straight or 58] d 653 734 mildly curved in section, its width being larger than the diamele 0 a 5 ter of a circular wire having the same cross sectional area and its thickness being smaller than said diameter. The plane which acts on the concrete is provided with projections for [56] References Cited spot welding in the formation of the wire cage. UNITED STATES PATENTS 5 Claims 24 Drawing Figures 891,234 6/1908 Crane ..52/734 WAIENTEMPRHIM Y 3.654.968

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amamsmzwamxammmw INVENTOR KATSUIIISA MIZUMA Attorneys STEEL WIRE CAGE WIRE FOR CIIEMICALLY PRESTRESSED CONCRETE PIPE BACKGROUND OF THE INVENTION The present invention relates to a steel wire orrod for use in chemically prestressed concrete pipe, which is effective for controlling the expansion of the expansion concrete therein over a wide range and with approximately uniform stress. In chemically prestressed concrete pipe, expansion concrete is caused to compensate for shrinkage of the concrete during hardening. A wire or rod restrains the force of the expansion so that a compressive stress occurs in the radial direction of the concrete during manufacture for the purpose of increasing the resistance of the pipe to external pressure.

The steel wire or rod is a member of a steel wire cage which is placed in a concrete frame during the manufacture of a concrete pipe. The steel wire is spirally wound and fixed around the periphery of a group of steel rods arranged parallel to one another longitudinally along the wall of a concrete pipe, and the internal surface of the steel wire serves to restrain the expansion of the expansion concrete.

Conventionally, a steel rod or wire circular in cross section has been used for this purpose. However, the area of the wire available to apply stress to the concrete under expansion is limited. Moreover, the stress applied to the concrete is not uniform over the external surface of the wire in contact with the concrete. A larger stress is imparted to the expansion concrete at the mid-portion than at extremes of the wire, and as the result, the expanding concrete in contact with the midportion of the wire may be fractured.

With these disadvantages in mind, it is an object of the present invention to provide a steel wire or rod adapted to apply a uniform compressive stress over a wide area to the concrete, thereby imparting to the concrete pipe a resistance to external pressures approximately percent higher than possible by use of a conventional circular wire having the same cross sectional area.

In the present invention, the width of the internal surface of the wire as wound spirally around the parallel steel rods to form the steel wire cage, i.e., the plane at which the compressive stress is applied on the concrete, is larger than the diameter of a circular wire with the same cross sectional area; its thickness is smaller than such diameter; and such internal surface is provided with projections to be spot welded to the parallel rods in the formation of the steel wire cage.

Other objects and features of the present invention will be made clear by the following description, taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial elevation of a known steel wire cage for use in chemically prestressed concrete pipe;

FIG. 2 is a partial section of a chemically prestressed concrete pipe under manufacture;

FIG. 3 is a section taken along line IIIIII of FIG. 2;

FIG. 4a is an elevation of a known wire for use in a steel wire cage of a chemically prestressed concrete pipe;

FIG. 4b is a section taken along line IVb-IVb of FIG. 4a;

FIG. 40 is an oblique view of another known wire;

FIG. 5a is an elevation of a steel wire in accordance with a first embodiment of the present invention;

FIG. 5b is a section taken along line VbVb of FIG. 5a;

FIG. 6a is a sectional illustration of the compressive stress created on concrete by the known wire illustrated in FIGS. 4a and 4b;

FIG. 6b is a sectional illustration of the compressive stress created on concrete by the novel wire illustrated in FIGS. 5a and 5b;

FIG. 7a is a partial section of the wire of FIGS. 5a and 5b positioned for spot welding;

FIG. 7b is a partial section of a wire of a second embodiment of the present invention positioned for spot welding;

FIG. 8a is an elevation of the wire of the second embodiment;

FIG. 8b is a section taken along line VIIIb-VIIIb of FIG. 8

FIG. 8c is a bottom view of the wire of FIG. 8a;

FIG. 9a is a section taken along line IXa-IXa of FIG. 9b illustrating a third embodiment of the present invention;

FIG. 9b is a bottom view of the wire of FIG. 9a;

FIG. 10a is a section taken along line XaXa of FIG. 10b illustrating a fourth embodiment of the present invention;

FIG. 10b is a bottom view of thewire of FIG. 100;

FIG. 11a is a sectional illustration of the compressive stress created on concrete by the known wire illustrated in FIGS. 40 and 4b;

FIG. 11b is a sectional illustration of the compressive stress created on concrete by the novel wire illustrated in FIGS. 80, 8b and FIG. 12 is a graph illustrating the relationship between steam curing time and steam temperature on a concrete pipe incorporating the novel wire of the present invention;

FIG. 13a is a sectional illustration of a concrete pipe in accordance with the present invention undergoing a pressure test; and

FIG. 13b is a longitudinal view, partially in section, of the arrangement of FIG. 13a.

Referring to FIGS. 1-3, the known method of manufacturing chemically prestressed concrete pipe will be described. FIG. 1 shows a known steel wire cage adapted to be placed in a concrete frame during the manufacture of chemically prestressed concrete pipe. The concrete includes a desired quantity of expansion cement, for example, 10-17% by weight. The frame is revolved whereby the concrete is hardened under the application of centrifugal force. The expansion of the expansion cement is restrained by the internal surface of the wire which is part of the steel wire cage. As a result, a compressive strees is applied in the radial direction of the concrete. The steel wire cage is usually formed as follows. The required number of steel reinforcing wires or rods 1 are arranged parallel to one another with their ends fixed to a holding means (not shown), and are spaced around the circumference of a drum 3. The rods 1 can move and revolve continuously along the outer circumference of drum 3. Around the outer circumference of rods 1 is spirally wound the hoop-reinforcing wire 2. This is done by relatively rotating the rod or the wire, i.e., by fixing either the group of steel rods or the hoop-reinforcing wire 2 and rotating the other. The points 4 where each rod 1 and the hoop-reinforcing wire 2 contact are successively and automatically spot-welded by an electrode 5, which electrode is connected to a power source E.

The reinforcing rods 1 and the hooping wire 2 preferably are made of a steel including elements as listed in Table 1.

The thus formed wire cage is placed as shown in FIGS. 2 and 3 into a concrete frame 6. Within section 6' of the frame, a concrete mixture including 10-17% by weight of expansion cement is poured. The concrete within section 6 of the frame is compacted under centrifugal force by rotating frame 6 together with rotating wheel 7, whereby the concrete is hardened to form a pipe. Wheel 7 is caused to rotate by any known suitable means, not shown.

After steam curing, the pipe is demolded and then submitted to underwater curing to produce a chemically prestressed concrete pipe. During the above mentioned concrete hardening process, the concrete containing the expansion concrete expands; and through restraint of this expansion by the internal surface of the hooping wire 2, a compressive stress is imparted in the radial direction of the pipe, thereby increasing the resistance of the pipe to external pressure.

As illustrated in FIGS. 4a-c, the conventional hooping wire consists of a steel rod or wire 2' circular in cross section. The wire illustrated in FIG. 40 differs from that illustrated in FIGS. 4a and 4b in that the former has axial notches 8 cut on the periphery thereof. But, both are circular in cross section. However, being circular in cross section, wire 2' is limited in the amount of stress it may impart to the concrete 9, as shown in FIG. 6a at f. Moreover, the stress applied to concrete 9 is not uniform over the periphery of the wire in contact with the concrete. More stress is applied at mid-portion C than at the ends. As a result, the concrete in contact with the mid-portion C may be fractured, resulting in a failure of the objective of the chemically prestressing manufacture, that is, to develop resistance to external pressure.

It has been discovered that the use of a wire 2" with a shape as illustrated in FIGS. 5a and 5b will eliminate the above-mentioned disadvantages. In FIGS. 5a and 5b, the plane is the internal surface which contacts the periphery of the rods 1 and restrains the concrete expansion. The width of plane 10 is larger than the diameter of a circular wire having the same cross sectional area as wire 2", and the thickness of wire 2" is less than such diameter. Plane 10 is preferably straight, however, it may be slightly concave or convex. The top 14 is preferably formed in a mild arc.

As seen by a comparison of FIGS. 60 and 6b, a wire of this profile has remarkable advantages over the previously known circular wire. Namely, whereas the circular wire has a limited ability to create compressive stress on the concrete 9 as indicated by f in FIG. 6a; the wire with the shape shown in FIGS. 5a and 5b has a much greater stress creating ability as shown by f in FIG. 6b. Furthermore, the stress acting on concrete 9 is approximately uniform over the entire surface 10, and accordingly there is no likelihood of the concrete being fractured as before.

A second embodiment of the present invention is shown in FIGS. 8a-8c and represents an improvement over the embodiment of the invention shown in FIGS. 5a and 5b. As shown in FIG. 7a when the wire of FIGS. 5a and b is wound around rods 1, the entire width of surface 10 contacts the rods. Due to this relatively large surface to surface contact, the spot welding of wire 2" to rods 1 is difficult with existing wire cage spot welders. This is due to the fact that the larger contact area requires longer weld time. Additionally, care must be taken not to deteriorate the mechanical properties of the wire during such welding. Thus, although the wire of FIGS. 5a and b is acceptable and gives vastly improved results, the embodiment of FIGS. 8a-b represents an even more desirable wire.

The width of the plane for applying a compressive stress to the concrete, i.e., the internal surface of the wire as wound spirally around the rods of the wire cage, is larger than the diameter of a circular wire having the same cross sectional area, and its thickness is smaller than such diameter. Also, the internal surface is provided with projections to facilitate spot welding during the formation of the wire cage.

In F IG. 8b, the internal surface of the wire as spirally wound around the rods, i.e., the plane 10 at which the compressive stress is applied to the concrete, is generally straight or midly curved in section and is provided at both ends with projections 13 and 13'. It is for the purpose of making the stress acting on the expansion concrete approximately even over the entire plane 10 that this plane 10 is formed straight or only midly curved. Thus, the width 12 of plane 10 is larger than the diameter of .a circular wire with the same cross sectional area, and its thickness 11 is smaller than such diameter. If the width 12 is equal to or smaller than the diameter of a circular wire with the same cross sectional area, and if the thickness 11 is equal to or larger than such diameter, a strong stress would be created on a small area of the concrete under expansion and the resultant adverse effects on the concrete would be as bad or even worse than if a wire of circular cross section were used. As shown in FIG. 8b, the top 14 is preferably formed in a mild arc. However, as illustrated in FIG. 5b, the top may be formed approximately straight in mid-portion, with both ends an ln thereof formed in mild arcs. As mentioned above, projections 13 and 13 enhance spot welding by providing relatively little surface to surface contact with rods 1, as shown in FIG. 7b. Provision of these projections 13 and 13' at both ends of plane 10, as shown in FIG. 8b, is desirable because it enhances the bending rigidity of wire 2, and the formed cage when laid on the ground therefore sufiers less deflection. However, the projections may satisfactorily be positioned within plane 10 symmetrically relative to the mid-point thereof as shown in FIG.

9a. Such arrangement likewise provides satisfactory spot welding. Furthermore, as illustrated in FIG. 10a, only a single projection may be provided on the plane 10. In this case, however, the projection must be provided on the bottom in a curved manner as illustrated by FIG. 10b. Otherwise, it would be difficult to obtain satisfactory spot welding, since it would be difficult to wind the wire on the drum, and during spot welding the wire would be inclined toward the steel rod.

The advantages of the present invention will now be illustrated with respect to a preferred example.

The preferred dimensions of the wire are, with reference to FIG. 8b: thickness 11, over 2.5 mm; width 12, at least 1.5 times the thickness 11; the curvature of the projections 13 and 13', l-2 R; height of the projections, 0.5-1.5 mm. When the thickness is less than 2.5 mm, a difficulty will sometimes arise in drawing the wire. The upper limit of the thickness 11 may be 5 mm or more. Width 12 may be less than 1.5 times the thickness 11, but better results would be obtained when it is more than 1.5 times the thickness. The upper limit of width 12 normally need not exceed four times the thickness 11. If the projections 13 and 13 are less than 0.5 mm in height, then during the formation of the wire cage when the spot welder 5 presses the wire 2 against the steel rod 1, the part of the plane 10 of the wire other than the projections 13 and 13' is likely to touch the rod 1. This would cause a small molten area to be formed on the wire, thereby causing deterioration of the mechanical properties of the wire. On the contrary, the projections may be over 1.5 mm in height. However, in view of the pressure of the wire on the periphery of rod due to the spot welder 5, the above-mentioned height would be sufficient to prevent the above-mentioned disadvantage during spot welding.

The chemical composition of the wire may be approximately the same as that of the known circular wire as listed in Table 1.

Raw steel of the above composition is held for 20 minutes at approximately 800 C.820 C. by the known method. The steel is then drawn to the shape according to FIG. 8b, and thereafter it may be submitted to bluing.

When a steel wire cage is formed by spot-welding as shown in FIG. 1, using the wire according to this invention, the wire 2 contacts through its projections 13 and 13 with the steel rod 1, as indicated in FIG. 7b. Thus, the projections 13 and 13 are welded to the opposite parts of the steel rods 1 by the spotwelder 5.

Spot welding may be accomplished with a spot welding current of LOGO-1,200 A using a known steel wire cage forming machine without any deterioration of the mechanical properties of the wire.

In the manufacturing process of chemically prestressed concrete pipe as described with reference to FIG. 2, the ability of a wire circular in cross section and having the same cross sectional area as a wire according to the present invention to stress the concrete is limited as shown by f in FIG. 110. However, a wire according to FIGS. 8a-c creates much more stress as shown by f in FIG. 11b. Thus, the strength of the chemically prestressed concrete pipe is increased by approximately 15% over that of a pipe using a circular wire with the same cross sectional area.

The above-mentioned advantages of the present invention may be illustrated by the following experiments:

1. Experimental conditions 1. Steel wire cage components l Hooping wire Raw steel having the chemical composition of Table 2 was held about 20 minutes at 800 C.-820 C. The steel was then drawn into a round wire 5 mm in diameter with a circular cross section. A second wire was made having the configuration shown in FIGS. 8a-c and having approximately the same cross sectional area (19.7 mm) as the above-mentioned circular wire. The dimensions of the second wire, with reference to FIG. 8b, were: width 12 was 6.3 mm; thickness 11 was 3 mm; the projections were 0.5 mm high; the projection top curvature was 1.5 R. The mechanical properties of both wires were the same, as listed in Table 3.

TABLE 2 C Si Mn P S 0.34% 0.25% 0.75% 0.030% 0.035%

TABLE 3 Tensile Yield load Tensile strength point Elongation 2.050 kg. I04 kgJmm. 94 kgJmm. 5.0%

2. Steel rod In both cases, m long circular rods each with a diameter of 5 mm. the chemical composition of Table 2 and the mechanical properties of Table 3 were used. Each steel rod group included 12 such rods.

3. Steel wire cage The two wires of (1) were each spirally wound around one of the steel rod groups of (2), using the method described with reference to FIG. 1. By spot welding the respective contacting point, two steel wire cages were formed. The outer diameters of the formed steel wire cages were about 600 mm, the axial length was 15 m, and the spiral pitch of the wound wire was 25 mm. These two steel wire cages were as indicated in FIG. 2 placed within concrete frames 6.

2. Concrete conditions The concrete poured into section 6' of the concrete frames had the same properties and volumes of aggregates and expansion cement in both cases as listed below.

1. The concrete was proportioned according to Table 4.

TABLE 4 Unit Unit Coarse aggregate Slump water cement Water maximum size volume volume cement 15 mm. l-S cm. I80 kg. 450 kg. 34%

Unit I Unit Unit fine aggrecoarse expansion gate aggregate cement 586 kg. 1,043 kg. 80 kg.

2. Properties of the aggregates conformed to Table 5.

I 1. After placing the above-mentioned two steel wire cages in sections 6 of their respective concrete frames, the known method of manufacture as described with reference to FIG. 2 was followed. Namely, after pouring the concrete as proportioned according to Tables 4-6 into sections 6' of the frames, the rotating wheel 7 was turned to rotate the frames 6, thereby centrifugally compacting the concrete. During such compaction, a centrifugal force of 5 G was applied to frames 6 for the initial 5 minutes, followed by gradual increases up to 35 G. This condition was maintained for Srninutes.

Following the compaction of concrete, the concrete was submitted to 3 hours of pre-curing; then steam curing as described with reference to FIG. 12 ensued. In FIG. 12, the ordinate is steam temperature (C.) and the abscissa is curing time (hour); and the dotted line represents the point at which the steam supply was stopped. In 15 hours after cessation of the steam supply, the pipes were demolded, then cured under water until tested. Thus, two chemically prestressed concrete pipes, l5 m long, 600 mm in outer diameter and 50 mm in wall t hickness, were produced.

4. External pressure resistance test of chemically prestressed concrete pipe. g The concrete pipes thus produced were respectively measured for resistance to external pressure in accordance with the following procedure described with reference to FIGS. 13a and 13b. Namely, the pipes 15 were laid flat on firm stands, rubber plates 16 and 16' about 20 mm thick were inserted at top and bottom of each pipe; additionally square blocks 17 of hard wood about 150 mm thick were added to the tops; steel beams 18 were placed on said blocks 17; thereafter using a hydraulic linear loading machine, the pipes were loaded vertically at their midpoint at a uniform increment rate of about 1,000 kg/m so that the loads might be evenly distributed. Meanwhile, dial gauges 20 were vertically attached at 150 mm from both ends of each pipe; and strain gauges l9 and 19 were internally plastered at 300 mm from both ends of each pipe. Through measurement of deflection and strain as recorded by these instruments, the cracking of the pipes was cv v s z .The chemically prestressed concrete pipe having a steel wire cage including the known wire having a circular cross section developed the first crack under a test load of 6500 Kg/m. However, the pipe having a cage including the wire as illustrated in FIGS. 8a-c and the same cross sectional area as the circular wire did not crack until a test load of 7500 Kg/m y asreached.

The above-mentioned test date on the external pressure resistance of such pipes have been confirmed by numerous other No'rE.-Gra.in size is given in of sieve retention.

3. Chemical composition of the expansion cement conloss due to strong heating in chemical analysis 3. Manufacturing process of chemically prestressed concrete pipe.

tests. For instance, raw steel with the chemical composition of able 2w s e b h eth d, e a ed in the above ample l (1) into wires with the shapes as illustrated in FIGS. 9 and l0and having dimensions as listed in Table 7. These wires had approximately the same mechanical properties listed in Table 3. The external pressure resistances of chemically prestressed concrete pipes embrasing steel wire cages built of these wires were compared with that of a pipe embracing a cage built of a known wire circular in section with nearly the same sectional area. The results of this comparison were practically the same as those test results mentioned above.

TABLE 7 Projection Top cur- Shape Thickness (ll) Width (12) vature Height As 2.4- mm. 1.4-4 l-ZR 0.5- FlG. 9 times the 1.5 mm.

thickness As 2.4-5 mm. 1.4-4 l-ZR 0.5- FIG. times the L5 mm.

thickness (Other test conditions were the same as in the above example) Thus it has been established that chemically prestressed concrete pipe having a steel wire cage built of the invented hooping wire is approximately superior in external pressure resistance than the pipe having a cage of the known hooping wire with the same cross sectional area.

Although several embodiments of the invention have been described in detail, such description is intended to be illustrative only, and not restrictive, since many details of the construction of the invention may be altered or modified without departing from the spirit or scope of the invention.

What is claimed is:

1. In a concrete pipe including a quantity of expansion cement and a wire cage to restrain the expansion force of said Exte i F d. wire Q38? sompt ja a P lF l y 9f thickness is at least 2.5 mm and said width is 1.5-4 times said parallel rods and a wire spirally mounted around the periphery of said rods, the inner surface of said wire acting to restrain said expansion force; the improvement wherein the width of said inner surface is larger than the diameter of a circular wire having the same cross-sectional area, the thickness of said wire is less than said diameter, said surface of said wire opposite said inner surface being formed in a mild arc, and said inner surface has continuous projection means for facilitating spot welding to said rods.

2. The improvement as claimed in claim 1, wherein said thickness.

3. The improvement as claimed in claim 2, wherein said means comprise a projection on each edge of said inner surface, each projection being 0.5-1.5 mm high and the surface of which is curved in the order of l-2 R.

4. The improvement as claimed in claim 2, wherein said means comprise two projections symmetrically located with respect to the midpoint of said surface, each projection being 0.5-1.5 mm high and the surface of which is curved in the order of l-2 R.

5. The improvement as claimed in claim 2, wherein said means comprise a curved projection centered with respect to the midpoint of said surface, said projection being 0.5-1.5 mm high and the surface of which is curved in the order of l-2 R. 

1. In a concrete pipe including a quantity of expansion cement and a wire cage to restrain the expansion force of said expansion concrete, said wire cage comprising a plurality of parallel rods and a wire spirally mounted around the periphery of said rods, the inner surface of said wire acting to restrain said expansion force; the improvement wherein the width of said inner surface is larger than the diameter of a circular wire having the same cross-sectional area, the thickness of said wire is less than said diameter, said surface of said wire opposite said inner surface being formed in a mild arc, and said inner surface has continuous projection means for facilitating spot welding to said rods.
 2. The improvement as claimed in claim 1, wherein said thickness is at least 2.5 mm and said width is 1.5-4 times said thickness.
 3. The improvement as claimed in claim 2, wherein said means comprise a projection on each edge of said inner surface, each projection being 0.5-1.5 mm high and the surface of which is curved in the order of 1-2 R.
 4. The improvement as claimed in claim 2, wherein said means comprise two projections symmetrically located with respect to the midpoint of said surface, each projection being 0.5-1.5 mm high and the surface of which is curved in the order of 1-2 R.
 5. The improvement as claimed in claim 2, wherein said means comprise a curved projection centered with respect to the midpoint of said surface, said projection being 0.5-1.5 mm high and the surface of which is curved in the order of 1-2 R. 